Interest in the use of liquid natural gas (LNG) as a motor vehicle fuel has increased dramatically in recent years. Whole fleets of government and industry vehicles have successfully been converted to natural gas, and some private individuals have converted their vehicles as well. Congress recently passed an energy bill which would require further increased use of alternative fuels in government and private fleets.
Several factors have influenced this increasing interest in natural gas as a motor vehicle fuel. LNG is relatively inexpensive. It also burns very cleanly, making it much easier for fleets to meet more restrictive pollution emission standards. However, handling LNG remains a significant problem.
Vehicles using LNG in place of gasoline are equipped with a cryogenic tank in place of an ordinary gas tank. A cryogenic tank is very well insulated and sealed. It is able to maintain the LNG at sufficient low temperatures for a period of time sufficient for a fleet vehicle to burn most of the LNG before significant vaporization occurs.
LNG fueling facilities are high capacity facilities generally designed to service large fleets of vehicles. A conventional LNG fueling station includes massive LNG storage tank, a pump for pumping the LNG, and a dispensing mechanism that includes a nozzle assembly that is used to connect and to disconnect quickly an LNG line to and from the cryogenic tank on the vehicle. The nozzle assembly includes a connector that is designed to quickly couple to and uncouple from a complementary connector on a receptacle on the vehicle's tank. Because LNG in its gaseous or vapor state is potentially explosive when mixed with air, valves located in each receptacle assure that no LNG or gaseous methane escapes from either of the connectors prior to complete coupling. Upon proper coupling, the valves are automatically displaced from their respective valve seats to allow LNG to flow in the vehicle's tank. A locking mechanism insures that the coupling halves are locked together prior to the opening of the valves and to prevent accidental disconnection of the receptacles during pumping.
LNG flowing through the nozzle assembly rapidly cools its exterior surface. Moisture in the atmosphere tends to condense and to freeze on the nozzle assembly. The ice is extremely undesirable, as it interferes with coupling of the nozzle to the receptacle on the motor vehicle. Ice also tends to form between the nozzle and the receptacle. Any ice that has accumulated on the nozzle assembly melts quickly at points of contact with the warmer receptacle. The moisture, in a liquid state, then spreads quickly and evenly. When cryogenic methane begins to flow through the receptacle, the moisture quickly re-freezes and effectively glues together the coupling, making it very difficult to detach the nozzle assembly from the vehicle receptacle. The ice can also form on the mechanical linkages of the latching mechanism, making it difficult to unlatch the nozzle.
The conventional solutions of removing ice are certainly inconvenient and, in the case of the hammer, potentially destructive and dangerous. Furthermore, breaking or melting of the ice is time consuming and slows refueling. Since LNG stations tend to be expensive to install and maintain, fleet operators often demand that LNG stations be capable of refueling at a rate of one vehicle every few minutes. Ice formation is thus an impediment to efficient operation of LNG refueling stations. It also discourages use of LNG dispensing stations by persons who are not specially trained, such as retail consumers, and therefore impedes more wide-spread acceptance of LNG as a fuel for motor vehicles.